1. Field of the Invention
The present invention relates to a biomass-derived epoxy compound and manufacturing method thereof.
2. Description of Related Art
From the viewpoint of carbon neutrality, vegetable- or plant-derived biomass has been expected as materials that do not cause global warming. The use of such plant-derived biomass has been attempted in resins, of which corn-derived thermoplastic poly(lactic acid)s have been mainly developed for practical use.
The use of such corn-derived thermoplastic poly(lactic acid)s, however, has not been spreading recently, because they suffer from resource conflict in the raw material corn with foodstuffs and they have low heatproof temperatures.
Accordingly, the current mainstream is to develop resins which use, as raw materials, “inedible resources” not conflicting with foodstuff and are highly resistant to heat. Among such inedible resources, ligneous wastes, i.e., unutilized trees, abound in Japan are expected as raw materials for biomass-derived resins.
Specifically, lignins have highly thermally stable polyphenol skeletons and are thereby expected to give biomass-derived thermosetting epoxy compounds, and these epoxy compounds in turn give epoxy resin compositions.
Lignins are plant-derived biomass and are firm or solid polymers containing propylphenols as backbone skeletons. Such lignins are classified by the process of extracting from trees typically as alkali lignins, Klason lignins, and steam explosion lignins.
Exemplary plant-derived biomass further includes lignophenols. The lignophenols have been prepared according to a technique of separating lignocellulose materials into lignophenol materials and carbohydrates (Patent Literature 1 (Japanese Patent Laid-open No. Hei 09-278904)). This technique utilizes a phase separation system developed by Prof. Masamitsu FUNAOKA (Mie University). As a result of the separation through the phase separation system, lignins are combined with phenols to give lignophenols. The resulting lignophenols are polyphenol resins that are linear molecules, have uniform structures, have a definite melting point of about 130° C., and are highly soluble.
To apply to various products, an epoxy resin composition should have satisfactory heat resistance properties and solubility. The solubility is required for the epoxy resin composition to be dissolved in an organic solvent to give a resin varnish, as described in Patent Literature 2 (Japanese Patent Laid-open No. Hei 09-235349). A prepreg is prepared by impregnating a base material with the resin varnish and drying the resulting article. Two or more plies of the prepreg are stacked, then thermally cured, and thereby yield products such as copper-clad laminates or insulating layers of motors. If a resin varnish contains an epoxy compound having insufficient solubility, it may often give a product unsatisfactory in properties such as heat resistance properties, because the ratio of the epoxy compound to a curing agent in the resin varnish may vary.
According to a known epoxidation process of a phenol compound, an epoxy compound having satisfactory solubility is prepared by adding an aqueous alkali metal solution to a solution of the phenol compound in epichlorohydrin and refluxing the resulting mixture (Non-Patent Literature 1 (H. Lee and K. Neville, “Handbook of Epoxy Resins”, McGraw-Hill, New York, 1960 pp. 2-3)). However, when a biomass-derived phenol compound is epoxidized according to the known epoxidation process, the resulting epoxy compound is substantially insoluble in organic solvents.
This is probably because the raw material biomass has a complicated structure including a wide variety of groups such as hydroxyl group, carboxyl group, carbonyl group, aldehyde group, and styryl group; an alkali metal used in the known process acts upon these groups to cause cleavage and re-polymerization of the material compound to thereby give an epoxy compound having an increased molecular weight; and the increased molecular weight acts to reduce the solubility of the epoxy compound (Non-Patent Literature 2 (“Advanced Technologies for Chemicals from Wood Resources”, CMC Publishing Co., Ltd., Tokyo Japan, 2007 pp. 53-56)).
The uses of epoxidized lignins as biomass-derived epoxy compounds are disclosed in Patent Literature 3 (Japanese Patent Laid-open No. 2005-199209) and Patent Literature 4 (Japanese Patent Laid-open No. 2006-066237).
Independently, the uses of epoxidized lignophenols as biomass-derived epoxy compounds are disclosed in Non-Patent Literature 3 (“Technologies for Higher Functionalities and for Recycling of Plant-derived Plastics” Science & Technology Co., Ltd., Tokyo Japan, 2007 pp. 129) and Patent Literature 5 (Japanese Patent Laid-open No. 2004-238539).
All these documents, however, fail to describe how to prevent biomass-derived epoxy compounds from increasing in molecular weight and how to allow them to have high solubility in organic solvents.